Basic Criminal Law –
The U.S. Constitution, Procedure,
and Crimes
By Anniken U. Davenport
CHAPTER 9: COMMON LAW
DEFENSES
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Chapter Objectives
 Know the common law defenses, and their
essential elements
 Understand the concept of self-defense and
be able to explain when non-deadly and
deadly force can be used
 Explain under what circumstances consent is
a defense
 Explain when mistake of law and mistake of
fact are defenses
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Chapter Objectives (cont’d)
 Explain entrapment
 Differentiate between the consequences
of voluntary and involuntary intoxication
 Explain the different standards for the
insanity defense and how each operates
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Sources of Defenses
 common law
 constitutional law
 statutory law
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Justification Defenses
 Used where the commission of the
proscribed act is justified and, therefore,
not appropriate for criminal sanctions.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Self-Defense
 A justification resting on the belief that
innocent people have the right to
protect themselves and their property
from crime.
 Each case is judged differently based on
the facts of that case.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Non-Deadly and
Deadly Force
 non-deadly force – a person may use a
reasonable amount of force to render an attacker
harmless
 deadly force – a person may only use deadly
force in self-defense when it reasonably appears
necessary to prevent immediate death or serious
injury or prevent the commission of a serious
felony involving risk to human life. Deadly force
may only be used against an attacker who has
initiated the aggression using unlawful force
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
The Retreat Rule
 Definition – generally, if a person is using deadly
force to stop a crime, he/she should always choose
to retreat if the opportunity to do so arises
 A person must retreat rather than use deadly
force unless the person is at his or her home or
business.
 Most states have adopted the rule that there is no
duty to retreat unless the retreat can be made in
complete safety.
 The attacker can also use the retreat rule if
he/she tried to make a withdrawal but the
defender continued to use force.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Doctrine of
Sudden Escalation
 If a fight that was not life threatening
suddenly becomes life threatening, the
initial aggressor can take whatever
action is necessary to protect himself.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Defense of Others
 A defendant can use the defense of
others defense when he acts in the
belief the intended victim had a legal
right to act in his or her own defense.
There need not be any special
relationship between the defendant and
the intended victim. In this case, the
defendant need not retreat unless he is
sure the victim is safe.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Defense of Property
 The law recognizes a difference between
defense of self and defense of property.
Generally, it is not appropriate to use deadly
force to defend objects unless a person is
also in immediate danger.

Katko v. Briney – the Iowa Supreme Court let
stand a jury verdict for actual and punitive
damages against the owner of an abandoned
farmhouse who had rigged a rifle to go off if an
intruder entered. An intruder did, and sued
successfully when he was injured
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Necessity Defense
 A justification defense that asserts that
it was necessary to break law in order
to prevent a more serious crime.
 The necessity defense can never be used
to justify a death to protect property.
 To use this defense, the defendant must
be without fault and cannot be in the
process of committing another crime at the
time the act was committed.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Duress Defense
 Duress is a defense if the defendant committed the
crime out of a well-grounded fear of death or serious
bodily harm.
• Required elements for a duress defense:
 the actor was wrongfully threatened by another to perform



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an act that he/she otherwise would not have performed;
and
the threat was of serious bodily harm or death to the
person or an immediate family member;
the threat was immediate and there was no way for the
threatened person to escape or avoid the threatened action;
the harm threatened was greater than the harm from the
crime committed; and
the threatened person was not intentionally involved in the
situation.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Mistake of Fact Defense

Used when a defendant honestly believes
something to be true that is not true.

The mistake of fact defense applies to different
crimes differently.




For general intent crimes the mistake must be a
reasonable mistake.
For specific intent crimes, any mistake of fact may be
used as a defense.
You could not form the specific intent to commit a crime
if you are mistaken about the facts.
The mistake of fact defense may not be used for strict
liability crimes.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Mistake of Law Defense

Used when a person in good faith relied
on an interpretation of law from a
person charged with administering the
law.

The mistaken interpretation of law may not
come from an attorney.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Entrapment


Used when law enforcement officials lure a person into
committing a crime.
two-pronged test for entrapment defenses


the criminal design must have originated with law enforcement
the defendant must not be predisposed to commit the crime;
some jurisdictions use different standards for determining
predisposition
 subjective standard, majority Rule – revolves around
the answer to one question, “Was the defendant
predisposed to commit the crime?”
 objective standard, minority rule – focuses on the
government’s inducement and asks the question, “Would
an innocent person be induced to commit the crime by the
officer’s acts?”
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Victim’s Consent

In some circumstances, the accused can
claim that the victim gave consent for the act
in question.

Reasons why a victim’s consent will not be valid







the victim is a minor
the victim has a mental disease or defect
the victim is intoxicated to the point he/she is unable to
make a reasonable judgment
consent is obtained by force or duress
consent is obtained by fraudulent or deceptive means
the victim has been judged to be legally incompetent
the consent defense is precluded by the law in question
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Capacity Defenses

May be used when the defendant lacks
the capacity or ability to control his or
her actions or understand that the act
was criminal in nature.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Infancy Defense

Infancy defense – Although some states have sought to
modify the standard by statute, under the common law, children
of tender age could not be held liable for criminal acts under the
presumption that they lacked the capacity to tell right from
wrong.

Under the common law standard:
 children under 7 years of age are conclusive presumed
incapable of knowing the wrongfulness of their crimes
 children 7-14 years of age have a rebuttable presumption of
incapacity. The burden of proof is on the prosecutor to prove
beyond a reasonable doubt that the defendant appreciated the
quality and nature of his/her actions.
 children over 14 were treated as adults and presumed to fully
appreciate the difference between right and wrong.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Intoxication Defense

involuntary intoxication – occurring when a
person unknowingly ingests an intoxicating substance;
most successful for the intoxication defense


persons who are involuntarily intoxicated are treated the
same as insane defendants
voluntary intoxication – occurring when a person
become willingly intoxicated; never used as a
defense for crimes of general intent


cannot be used as an excuse or justification of a crime of
homicide, to crimes involving negligence, recklessness, or
strict liability
has been used as a defense to specific intent crimes where
the intoxication prevents the Defendant from formulating
the requisite intent
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Insanity Defense

A defendant using the insanity defense
is claiming he/she lacked the mental
state to understand the nature and
consequences of the crime. If the
defendant is successful, he/she would
be committed to a mental hospital
rather than prison. The defendant
would remain there until the state
determined the person to be sane.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
M’Naghten Rule

The burden of proof for the insanity
defense is that “Every man is presumed
to be sane and to possess a sufficient
degree of reason to be responsible for
his crimes, until the contrary be proved
to (the jury’s) satisfaction; and that to
establish a defense on the ground of
insanity, it must be clearly proved.”
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Insanity Defense



In 1886, Alabama adopted the more liberal “irresistible
impulse” test. In effect, this created a “temporary
insanity” for people who committed “crimes of passion.”
Durham Test – only requires a “substantial lack of
capacity; part of the Model Penal Code, but has not
been adopted by all states.
guilty, but mentally ill – under special laws enacted
in some states, defendants who do not meet the
M’Naghten standard of a complete lack of capacity, but
fall under the substantial lack of capacity standard are
convicted and sent to a mental hospital; if they recover,
they are sent to prison for the rest of their term.
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Capacity to Stand Trial

definition– Common law has long held that a person
must be able to understand the proceedings against him
and be able to interact with his attorneys in order have a
fair trial.
 If a defendant claims lack of capacity, the state must:
 try the defendant, if he or she is competent to
stand trial,
 dismiss the charges, or
 commence civil proceedings to have the defendant
committed to a mental institution
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Competency Standard
 The standard for competency in many jurisdictions
comes from Justice Thurgood Marshall’s dissent in
White v. Estelle, where he stated: “This Court has
approved a test of incompetence which seeks to
determine whether the defendant ‘has sufficient
present ability to consult with his lawyer with a
reasonable degree of rational understanding–and
whether he has a rational as well as factual
understanding of the proceedings against him.’
Dusky v. United States, 362 U. S. 402 (1960).”
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved
Incapacity and Punishment


In cases where the death penalty has already
been imposed, convicts can postpone
execution by claiming insanity just prior to
execution.
In other cases, involving the imposition of
time in prison, should insanity during
incarceration occur, prisoners are moved to
a psychiatric hospital for the remainder of
their term. Should they still be insane at the
end of their term, they may be committed to
a mental hospital until they recover
Davenport: Basic Criminal Law, 2nd ed.
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All rights reserved